Torque converter clutches are known to increase efficiency of a torque converter under certain driving conditions. In a typical configuration, the clutch is hydraulically applied to bypass a fluid circuit of the torque converter. While maximum efficiency of an typical torque converter fluid circuit is about 92%, the efficiency of a typical torque converter clutch can approach 100%. Therefore, the torque converter clutch can be applied to increase the fuel economy of a vehicle drivetrain.
The transmission must maintain a minimum hydraulic pressure in the torque converter fluid circuit to prevent cavitation. Typical torque converters are configured such that the fluid circuit pressure also acts as a back pressure on the torque converter clutch, opposing the clutch apply pressure. Therefore, the transmission pump must work harder to increase the clutch apply pressure to overcome the back pressure. This work may negate some of the fuel economy benefit gained by engaging the torque converter clutch.